Periodically patterned films exhibit strong resonance effects that originate in quasi-guided, or leaky, waveguide modes [1-7]. With thickness and period on the order of the wavelength, these compact elements yield versatile electromagnetic spectra and surface-localized energy states with controllable Q factors. Using powerful electromagnetic design methods, the spectral bands of these sub wavelength resonant leaky-mode elements can be engineered to achieve photonic devices with practical attributes. We note that the terms “photonic,” “optical” and “electromagnetic” may be used interchangeably herein. For example, a single periodic layer with one-dimensional periodicity enables narrow-line filters, polarizers, reflectors, and polarization-independent elements [8].
A polarizer is an optical device that passes an electromagnetic wave with one particular polarization state and blocks all other states. Polarizers are essential in diverse photonics applications including display [9], microscopy [10], polarimetric astrophysical observation [11], laser machining [12], and quantum information processing [13]. In particular, nanostructured and sub wavelength polarizers offer compact integrability [14,15], thermal stability in high-power systems [12,16], and space-variant vector beam generation [17,18].
Conventional polarizers based on natural crystals and multilayer thin films are commonplace. Dichroic polarizing crystals absorb light with particular polarization along a defined crystal axis permitting another state to survive. Multilayer thin films are used in polarizing beam splitters at particular angles of incidence; they are not useful at normal incidence. Wire-grid polarizers (WGPs) are made with parallel grids of wires that have nanoscale spatial features for visible light wavelengths. Wire grid polarizers are in wide practical use and sold commercially by several suppliers. In the ˜300-4000 nm spectral region, the grids may be glass-slide enclosed whereas in the 4-12 μm region they are often silicon supported. The WGPs operate in transmission and work by absorbing and reflecting the polarization state with the electric-field vector along the wires. WGPs are wideband and transmit typically more than 75% of the input light that is in the desired polarization state. Advantages of devices not based on metals, such as those disclosed, include low loss and attendant high efficiency and ability to work as good polarizers in reflection, transmission, or both.
Sub wavelength periodic thin-film polarizers fashioned in dielectric media provide robust high-power performance and feasible fabrication in most practical frequency domains. Innovative polarizers have been implemented by combining multilayer films with linear sub wavelength gratings to induce polarization selectivity at normal incidence [19, 20]. Advanced polarizer designs in simple architecture were subsequently demonstrated engaging guided-mode resonance effects [21-23]. These devices operate with a broadband resonant reflection in one polarization state and concomitant transmission in the orthogonal state.
What is needed is the ability for nanowire grid polarizers to strongly polarize incident light in reflection and transmission across considerable spectral and angular levels. Nano wire grid is invisible in Transverse-Magnetic (TM) polarization while it resonates effectively in Transverse-Electric (TE) polarization. All these are achieved by minimal material embodiment that is mostly empty space. This polarizer is feasible in wide spectral domains including the near-infra red, THz and longer wavelength regions.